Electrical apparatus



Jan. 21, 1936. F; M, A K 2,028,589

ELECTRICAL APPARATUS Filed Dec, 21, 1932 Fig.2.

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30 wave length, preferably an amber glass, not affect the type ofmineral insulating oil in Patented Jan. 21. 1936 2,028,589

llNlTED STATES PATENT OFFICE 2,028,589 ELECTRICAL APPARATUS Frank M.Clark, Pittsfield, Mass., assignor to General Electric Company, acorporation of New York I Application December 21, 1932, Serial No.648,286

4 Claims. (Cl. 220-82) The present invention relates to encased electoindicate the level of the liquid inside the trical apparatus, such forexample as transtank and easing formers, X-ray outfits, high tensionbushings, The high voltage bushing I6, as shown in and in generaldevices which are insulated and greater detail in Fig.2, includes aporcelain shell 5 cooled by liquid dielectric material which is sub- I!which is filled with insulating oil E8 in which ject during use tochemical change, such as is immersed a conductor l9 connecting thebushmineral hydrocarbon oil. i ing terminal 28 with the transformer inthe eas- Casings for such apparatus sometimes are ing Ill. The oil I8extends up into and partially made partly of transparent glass, in orderto fills a transparent liquid level gauge M to a '10 permitascertainment of a condition of the l v l 2- 'Th au e 2 a o e v s a anexin liquid dielectric material, such for example as p s chamber toPermit expansion a 00 1- its level, its fluidity, or the presence orabsence traction of the oil 3 in the shell I! due to in it of sludge.Sludge is a semi-solid material p re C which forms during use. It isdeleterious to the Transformers are Often used n locations exdielectricproperties of oil and renders it less posed to Sunlight, the e D SHbeing some- 15 m i t as liquid h' medium, times to indirect sunlight butmore often being I have discovered that appreciable damage to nt ns di tsu t h s n 0. p p .results to liquid dielectric material which is subll,expansion tank I? nd bushing Shell H are ject to acid and sludgeformation when exposed formed Q Opaque materials 5 that the insuin suchapparatus to the chemical action of light letihg Oil in these parts S.p0teeted f om out- 20 of relatively short wave length. While no sharp s dl ht- H w v th iqu d l v l au es 5 critical limit of wave length can bedesignated, d 2| m s e m de of t ansparent material the most deleteriouseffect appears to be due to in ordel'thet the levels and 22 0f the q dlight below about 600 millimicrons of wave may be Visibleus, h Sma lVolume of oil 25 1ength.- In accordance with my invention this n thesegauges I d 2| s e s ly exposed 25 harmful effect is obviated while stillgiving view to any direct indirect lightwhieh eac s to the liquiddielectric material by the use, as the gaugesa part of the casing, ofcolored transparent ma- I have diSOO'l/eled that light having Wave t -11 which is opaque t light of harmful t; lengths greater than about 600millimicrons does The invention will be more fully explained whichelectrical lepperetus is Commonly min the following description taken inconnecmersed but that light having Substantially m ith th accombanyjngdrawing in which shorter wave lengths will cause such oil to de- Fig. 1is a front elevation view of an encased If this permitted to ppen, the

35 liquid insulated transformer with a high voltage" depreeietedieilwill radually d fiuse and mix 5 bushing of .th 114mm type; Fig 2 is anwith the good 011 with which it is in communilarged View of t upper endof t e high t cation in the main casing l0 and in the bushage bushingwith parts broken away to indicate ihg Shell I the structure moreclearly, and Figs. 3, 4, and 5 The effect of the light of the shorterWe've are graphs indicating the relative efiect on oil lengths is toCause chemical changes in he 011, 40 of clear and amber glass as acontainer material. and acids and Sludge are Produced- These Likereference characters indicate similar parts duce the dielectric strengthof the attack in Figs. 1 and 2 of the drawing. solid material (resins,pitch and the like) used Th tran former casing 10 shown in Fig 1 asinsulation in the electrical apparatus imthedrawing isin communicationthrough a pipe mersed in the oil and the sludge is deposited on 45 IIwith an expansion tank I2 to permit expansion the apparatusso that it isweakened electrically and contraction due to temperature changes of d, hp d during i Opera ion is less mineral oil or such liquid dielectricmaterial as efllcien ly dissip may be employed in the casing Ill. Thetank Some of the effects of light passing through Ill, pipe II andexpansion tank I: are filled; ordinary c e r l ss a made v d t by thee0with such liquid to a level l3 in the expansion graphs shown in Figs. 3,4, and 5. The absence tank and the space above the liquid is in c0mofeffe t O the Oil y light passing g munication with the outside airthrough a amber glass also is indicated. In Figs. 3 and 4 breather M.The expansion tank I2 is prois indicated the progressive change in colorand vlded with a transparent liquid level gauge is acidity due toexposure of oil to light passing 2 aoasisse by amber glass noappreciable color or acidity change could be noted'for the same periodof time. i

The formation of sludge under the influence of light is even more markedthan the color change and acid formation. As shown in Fig. 5,

a rapid increase of potential sludge occurs in the oil. Sludge whenfirst formed in mineral oil tends to be held in suspension or solution,but, of course, accumulates, and eventually becomes precipitated. Thesludging produced by exposure to light transmitted by clear glass over aperiod of about ten weeks (as indicated by the legend Sludge in Fig. 5)and referred to above as potential sludge can be made evident by thesocalled bomb test. In accordance with it, samples of oil to be testedare subjected in a bomb at a temperature of 140 C. for about 24 hours tooxygen gas at a pressure of about 250 pounds to the square inch. Anysludge formed under these conditions is centrifugally separated andobserved, and measured. As made evident by Fig. 5 oil subjected underthe test conditions only to light transmitted by amber glass showedhardly an appreciable tendency to sludge as shown by the bomb test.

In order to prevent or reduce these undesirable results, the liquidlevel gauges l5 and 2| are formed of material, which is opaque to lightrays having wave lengths shorter than about 600 millimicrons. Whileamber glass is preferred, red glass or glass of other color cutting ofithe 1 short wave lengths of light may be employed.

Harmful light is thus prevented from reaching the oil and light of thevisible spectrum having wave lengths substantially longer than 600millimicrons clearly discloses the level of the oil but does not harmthe oil.

The invention has been explained in connection with a particular.application thereof but it will be apparent that other applications andchanges may bemade without departing from the spirit of the inventionand the scope of the appended claims.

For example, parts of the casing of a fluidcooled electrical deviceother than a level indicator or gauge may be made of glass having a'coloradapted to intercept the undesirably actinic short wave lengths. Avarnish or other coating of suitable color on a clear glass may beemployed within the scope of my invention.

What I claim as new and desireto secure by Letters Patent of the UnitedStates, is:

1. In'electrical apparatus, a casing, an electrical conductor in saidcasing, a body of mineral insulating oil in said casing for insulatingsaid conductor, oil level indicating means comprising a portion of saidcasing, said portion having the capacity to transmit light, said oilbeing exposed to light passing through said light transmitting portion,and means for substantially restricting transmission of light throughsaid portion to wave lengths in excess of 600 millimicrons to reduce thedepreciation .of the insulating value of said oil.

2. In electrical apparatus, a casing, an electrical conductor in saidcasing, a body of mineral insulating oil in said casing for insulatingsaid conductor, an oil level indicating means comprising a portion ofsaid casing having the capacity .to transmit light, said oil beingexposed to light passing through the said light transmitting portion,and means including an amber glass member for preventing the passagethrough said portion of wave lengths of light having a depreciatingeffect on the insulating value of said oil.

' 3. In'electrical apparatus, a casing, an electrical conductor in saidcasing, efibody of mineral oil in said casing for insulating saidconductor,

an oil-level indicating means comprising a portion of said casing havingthe capacity to transmit light, said oil being exposed to light passingthrough said light transmitting portion, and

means including ared glass member for preventing the passage throughsaid portion of wavelengths of light having a depreciating effect on theinsulating value of said oil. 4. A high tension electrical transformerbushing comprising a casing, an electrical conductor in said casing, a-'body of mineral oil in said casing 'for insulating said conductor, aliquid level gauge glass in the wall of said casing, said gaugeglass'being composed of amber glass whereby wavelengths of light havinga'depreciating effect on the insulating value of said oil aresubstantially excluded from said casing.

FRANK M. CLARK. I

